A fallacy is a bad argument. Below are a number of what are called
informal
fallacies, common problems of reasoning that you will find in careless
arguments.

Post hoc ergo propter hoc fallacy ("after that, therefore
because
of that") -- a faulty or assumed cause-effect relationship that doesn't
necessarily
hold. Example: The fact that the Bush administration has sold the
rights
to clean up the oil fields in Iraq to Halliburton proves that the war
was
about oil after all.

Hedging or equivocation -- changing the meaning of a word or concept
from
one part of an argument to the next. Example: We can never stop war,
since
even in families there are sometimes wars.

Red herring -- a decoy, an idea that is tossed into the argument to
lead
the line of reasoning in an irrelevant direction (from the practice of
dragging
a herring across a trail to throw off the scent in a hunt). Example: We
haven't
yet found any weapons of mass destruction in Iraq,
but Syria is a potential problem, don't you think?

Ad hominem attack -- ("against the man") Attacking or
criticizing
the person rather than his ideas. Example: Our philosophy professor is
against
the war, but what can you expect? She's a Deadhead and wears a backpack
to
class.

"Either-or" fallacy (also called "false dilemma") -- Giving or acting
as
if there are only two choices when in fact there are more than two
choices.
Example: In the current world situation, regarding terrorism, you are
either
with us or you're against us.

"Bandwagon" fallacy (also called "appeal to common practice or
common
belief" ) -- accepting an idea because everyone else believes it or
assumes
it. Example: We went after Saddam because of 9/11.

Appeal to false authority -- accepting an idea because someone you like
accepts
it, whether or not that person has the authority to know. Example:
Martin
Sheen is against the war and he plays the President on TV so I'm with
him.

"Slippery slope" fallacy -- jumping to conclusions on the basis of one
event
or connection. Example: If we had left Saddam in power, next
every other despot in the region would get overconfident, then all the
ones in Latin America and Africe, and before
you know it we'd be threatened by the entire Third World.

"Straw man" or "Straw Dog" fallacy -- Putting words in someone's mouth
to
make them look bad or depicting them or their ideas in such a
caricatured
way as to trivialize them or their ideas. Example: Anti-war protestors
walk around with their scruffy hair, slovenly dress, and sloppy
thinking saying "Peace" like that was somehow a solution to world
political problems.